Method for forming carbon nanotube structure

ABSTRACT

A method for making a carbon nanotube structure includes providing a substitute substrate, a growing substrate, and a carbon nanotube array, the carbon nanotube array grown on the growing substrate. A carbon nanotube structure can be drawn from the carbon nanotube array. The carbon nanotube structure includes carbon nanotube segments joined end-to-end. The carbon nanotube array is transferred from the growing substrate onto the substitute substrate. During transfer, structural integrity of the carbon nanotube array is maintained. The carbon nanotube structure is drawn from the carbon nanotube array transferred onto the substitute substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201410124617.4, filed on Mar. 31, 2014 inthe China Intellectual Property Office, the contents of which are herebyincorporated by reference. This application is related to applicationentitled, “METHOD FOR TRANSFERRING CARBON NANOTUBE ARRAY AND METHOD FORFORMING CARBON NANOTUBE STRUCTURE”, filed Jun. 20, 2014 Ser. No.14/310,310.

FIELD

The subject matter herein generally relates to methods for formingcarbon nanotube structures.

BACKGROUND

Carbon nanotube can be fabricated by drawing from a carbon nanotubearray grown on a growing substrate (e.g., silicon wafer), as disclosedby U.S. Pat. No. 8,048,256 to Feng et al. The carbon nanotube film isfree standing and includes a plurality of carbon nanotubes joinedend-to-end by van der Waals attractive force therebetween. The carbonnanotubes in the carbon nanotube film are substantially aligned alongthe lengthwise direction of the carbon nanotube film, and thus, thecarbon nanotube film has good thermal and electrical conductivity alongthe direction of the aligned carbon nanotubes. The carbon nanotube filmis substantially transparent and can be used as a conductive thin film.Therefore, the carbon nanotube film can be used in many differentfields, such as touch panels, liquid crystal displays, speakers, heatingdevices, thin film transistors, cables, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures, wherein:

FIG. 1 is a schematic structural view of an embodiment of a method forforming a carbon nanotube structure.

FIG. 2 shows a scanning electron microscope (SEM) image of a carbonnanotube film drawn from a carbon nanotube array.

FIG. 3 shows carbon nanotubes joined end-to-end.

FIG. 4 shows an optical photo of drawing the carbon nanotube film fromthe carbon nanotube array transferred to a substitute substrate.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “another,” “an,” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean “at leastone.”

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures and components have notbeen described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts havebeen exaggerated to better illustrate details and features of thepresent disclosure.

Several definitions that apply throughout this disclosure will now bepresented.

The term “contact” is defined as a direct and physical contact. The term“substantially” is defined to be essentially conforming to theparticular dimension, shape, or other description that is described,such that the component need not be exactly conforming to thedescription. The term “comprising,” when utilized, means “including, butnot necessarily limited to”; it specifically indicates open-endedinclusion or membership in the so-described combination, group, series,and the like.

Referring to FIG. 1, the present disclosure is described in relation toa method for forming a carbon nanotube structure 40.

In block S1, a substitute substrate 30 and a growing substrate 20 areprovided. The growing substrate 20 has a carbon nanotube array 10 grownthereon, and the carbon nanotube array 10 is in a state that is capableof having the carbon nanotube structure 40 drawn therefrom.

In block S2, the carbon nanotube array 10 is transferred from thegrowing substrate 20 onto the substitute substrate 30. The state of thecarbon nanotube array 10 before, during, and after the transfer onto thesubstitute substrate is still capable of having the carbon nanotubestructure 40 drawn therefrom.

In block S3, the carbon nanotube structure 40 is drawn from the carbonnanotube array 10 on the substitute substrate 30.

The carbon nanotube structure 40 can be a free-standing structureincluding a plurality of carbon nanotubes joined end-to-end by van derWaals attractive force therebetween. The carbon nanotube structure 40can be a carbon nanotube film or a carbon nanotube wire.

The carbon nanotube array 10 is grown on the growing substrate 20 by achemical vapor deposition (CVD) method. The carbon nanotube array 10includes a plurality of carbon nanotubes oriented substantiallyperpendicular to a growing surface of the growing substrate 20. Thecarbon nanotubes in the carbon nanotube array 10 are closely bondedtogether side-by-side by van der Waals attractive forces. By controllinggrowing conditions, the carbon nanotube array 10 can be essentially freeof impurities such as carbonaceous or residual catalyst particles.Accordingly, the carbon nanotubes in the carbon nanotube array 10 areclosely contacting each other, and a relatively large van der Waalsattractive force exists between adjacent carbon nanotubes. The van derWaals attractive force is so large that when drawing a carbon nanotubesegment (e.g., a few carbon nanotubes arranged side-by-side), adjacentcarbon nanotube segments can be drawn out end-to-end from the carbonnanotube array 10 due to the van der Waals attractive forces between thecarbon nanotubes. The carbon nanotubes are continuously drawn to form afree-standing and macroscopic carbon nanotube structure 40, which can bein the shape of a film or a wire. The carbon nanotube array 10 that canhave the carbon nanotube structure 40 drawn therefrom can be a superaligned carbon nanotube array. A material of the growing substrate 20can be P-type silicon, N-type silicon, or other materials that aresuitable for growing the super aligned carbon nanotube array.

Referring to FIG. 2 and FIG. 3, the carbon nanotube structure 40 drawnfrom the carbon nanotube array 10 includes a plurality of carbonnanotubes joined end-to-end and can be a free-standing carbon nanotubefilm. The carbon nanotube film includes a plurality of carbon nanotubessubstantially aligned along the same direction.

The carbon nanotube film can include or consist of a plurality of carbonnanotubes. In the carbon nanotube film, the overall aligned direction ofa majority of the carbon nanotubes is substantially aligned along thesame direction parallel to a surface of the carbon nanotube film. Amajority of the carbon nanotubes are substantially aligned along thesame direction in the carbon nanotube film. Along the aligned directionof the majority of carbon nanotubes, each carbon nanotube is joined toadjacent carbon nanotubes end to end by van der Waals attractive forcetherebetween, whereby the carbon nanotube film is capable of beingfree-standing structure. There may be a minority of carbon nanotubes inthe carbon nanotube film that are randomly aligned. However, the numberof the randomly aligned carbon nanotubes is very small and does notaffect the overall oriented alignment of the majority of carbonnanotubes in the carbon nanotube film. Some of the majority of thecarbon nanotubes in the carbon nanotube film that are substantiallyaligned along the same direction may not be exactly straight, and can becurved at a certain degree, or not exactly aligned along the overallaligned direction by a certain degree. Therefore, partial contacts canexist between the juxtaposed carbon nanotubes in the majority of thecarbon nanotubes aligned along the same direction in the carbon nanotubefilm. The carbon nanotube film can include a plurality of successive andoriented carbon nanotube segments. The plurality of carbon nanotubesegments are joined end to end by van der Waals attractive force. Eachcarbon nanotube segment includes a plurality of carbon nanotubessubstantially parallel to each other, and the plurality of paralleledcarbon nanotubes are in contact with each other and combined by van derWaals attractive force therebetween. The carbon nanotube segment has adesired length, thickness, uniformity, and shape. There can beclearances between adjacent and juxtaposed carbon nanotubes in thecarbon nanotube film. A thickness of the carbon nanotube film at thethickest location is about 0.5 nanometers to about 100 microns (e.g., ina range from 0.5 nanometers to about 10 microns). When the carbonnanotube structure 40 has a small width, the carbon nanotube structure40 can be a free-standing carbon nanotube wire.

The term “free-standing” includes, but is not limited to, a carbonnanotube structure 40 (e.g., film or wire) that does not need to besupported by a substrate. For example, a free-standing carbon nanotubestructure 40 can sustain the weight of itself when it is hoisted by aportion thereof without any significant damage to its structuralintegrity. If the free-standing carbon nanotube structure 40 is placedbetween two separate supporters, a portion of the free-standing carbonnanotube structure 40 suspended between the two supporters can maintainstructural integrity. The free-standing carbon nanotube structure 40 isrealized by the successive carbon nanotubes joined end to end by van derWaals attractive force.

In the present disclosure, the growing of the carbon nanotube array 10and the drawing of the carbon nanotube structure 40 are processed ondifferent structures (i.e., the growing substrate 20 and the substitutesubstrate 30). The substitute substrate 30 for drawing the carbonnanotube structure 40 can be made of low-price materials, and thegrowing substrate 20 can be recycled quickly. Thus, production of thecarbon nanotube structure 40 can be optimized.

The substitute substrate 30 can be a soft, elastic, or rigid solidsubstrate. The substitute substrate 30 has a surface to accept thecarbon nanotube array 10 thereon. During transferring of the carbonnanotube array 10 from the growing substrate 20 to the substitutesubstrate 30, the state of the carbon nanotube array 10 is still capableof drawing the carbon nanotube structure 40 from the carbon nanotubearray 10 on the substitute substrate 30. That is, the carbon nanotubearray 10 transferred to the substitute substrate 30 is still a superaligned carbon nanotube array.

In one embodiment, the carbon nanotube array 10 can be transferred tothe substitute substrate 30, so that the carbon nanotube array 10 isoriented the same as on the growing substrate 20.

In another embodiment, the carbon nanotube array 10 is arranged upsidedown on the surface of the substitute substrate 30. The carbon nanotubesare grown from the growing surface of the growing substrate 20 to formthe carbon nanotube array 10. The carbon nanotube includes a bottom endadjacent or contacting the growing substrate 20 and a top end away fromthe growing substrate 20. The bottom ends of the carbon nanotubes formthe bottom surface 102 of the carbon nanotube array 10, and the top endsof the carbon nanotubes form the top surface 104 of the carbon nanotubearray 10. After the carbon nanotube array 10 is transferred to thesubstitute substrate 30, the top surface 104 of the carbon nanotubearray 10 is now adjacent to or contacting the substitute substrate 30,and the bottom surface 102 of the carbon nanotube array 10 is now awayfrom the substitute substrate 30.

In block S2, the carbon nanotube array 10 can be transferred from thegrowing substrate 20 to the substitute substrate 30 at room temperature(e.g., 10° C. to 40° C.). Block S2 can include blocks S21 and S22.

In block S21, the substitute substrate 30 and the carbon nanotube array10 on the growing substrate 20 are brought together such that thesurface of the substitute substrate 30 and the top surface 104 of thecarbon nanotube array 10 are contacting each other.

In block S22, the substitute substrate 30 and the growing substrate 20are moved away from each other, thereby separating the carbon nanotubearray 10 from the growing substrate 20.

The surface of the substitute substrate 30 and the top surface 104 ofthe carbon nanotube array 10 can be bonded by van der Waals attractiveforces, and a bonding force (F_(BC)) between the carbon nanotube array10 and the substitute substrate 30 is smaller than the van der Waalsattractive forces (F_(CC)) between the carbon nanotubes in the carbonnanotube array 10. Meanwhile, the F_(BC) is larger than the bondingforce (F_(AC)) between the carbon nanotube array 10 and the growingsubstrate 20, to separate the carbon nanotube array 10 from the growingsubstrate 20. Therefore, F_(AC)<F_(BC)<F_(CC) must be satisfied.

To satisfy F_(AC)<F_(BC)<F_(CC), the substitute substrate 30 can have asuitable surface energy and a suitable interface energy can existbetween the substitute substrate 30 and the carbon nanotube array 10.Thus, the substitute substrate 30 can generate enough bonding force(e.g., van der Waals attractive force) with the carbon nanotube array 10simply by contacting the carbon nanotube array 10. A suitable materialof the substitute substrate 30 must have a sufficient bonding forceF_(BC) (e.g., van der Waals attractive force) with the top surface 104of the carbon nanotube array 10 to overcome the bonding force F_(AC)between the carbon nanotube array 10 from the growing substrate 20. Thesurface of the substitute substrate 30 can be substantially flat. In oneembodiment, the material of the substitute substrate 30 ispoly(dimethylsiloxane) (PDMS).

The substitute substrate 30 can adhere to the carbon nanotube array 10without an adhesive binder and only by van der Waals attractive forces.Although the adhesive binder can have a bonding force with the carbonnanotube array greater than the bonding force between the carbonnanotube array 10 and the growing substrate 20, because the van derWaals attractive force between the carbon nanotubes in the carbonnanotube array 10 is small, the adhesive binder must have a bondingforce with the carbon nanotube array 10 sufficiently less than thebonding force F_(CC) between the carbon nanotubes in the carbon nanotubearray 10. Otherwise, the carbon nanotube structure 40 cannot be drawnfrom the transferred carbon nanotube array 10.

In blocks S21 and S22, the substitute substrate 30 can always be in asolid state.

In block S21, to ensure almost all the top ends of the carbon nanotubesin the carbon nanotube array 10 have sufficient contact with the surfaceof the substitute substrate 30, a pressing force (f) can be applied tothe carbon nanotube array 10 by the substitute substrate 30. Thepressing force f cannot be too large to ensure the state of the carbonnanotube array 10 is still capable of drawing the carbon nanotubestructure 40 when transferred to the substitute substrate 30. Thepressing force can satisfy 0<f<2N/cm². The direction of the pressingforce can be substantially perpendicular to the growing surface of thegrowing substrate 20 (i.e., along the length direction of the carbonnanotubes). The pressing force is not to press the carbon nanotubes downor vary the length direction of the carbon nanotubes in the carbonnanotube array 10, otherwise the state of the carbon nanotube array 10could change. During the pressing of the carbon nanotube array 10, thecarbon nanotubes in the carbon nanotube array 10 are still substantiallyperpendicular to the growing surface of the growing substrate 20.

In block S22, a majority of the carbon nanotubes in the carbon nanotubearray 10 can be detached from the growing substrate 20 at the same timeby cutting means, or moving either the substitute substrate 30 or thegrowing substrate 20, or both, away from each other along a directionsubstantially perpendicular to the growing surface of the growingsubstrate 20. The carbon nanotubes of the carbon nanotube array 10 aredetached from the growing substrate 20 along the growing direction ofthe carbon nanotubes. When both the substitute substrate 30 and thegrowing substrate 20 separate, the two substrates both moves along thedirection perpendicular to the growing surface of the growing substrate20 and depart from each other.

Referring to FIG. 4, in the block S3, the carbon nanotube structure 40is drawn from the carbon nanotube array 10 that was transferred to thesubstitute substrate 30, not from the carbon nanotube array 10 locatedon the growing substrate 20. In one embodiment of block S3, the carbonnanotube structure 40 can be drawn from the carbon nanotube array 10upside down on the surface of the substitute substrate 30 (i.e., drawnfrom the bottom surface 102 of the carbon nanotube array 10).

Block S3 can include block S31 and S32:

In block S31, a carbon nanotube segment having a predetermined width isdrawn from the carbon nanotube array 10 on the substitute substrate 30.The segment is selected using a drawing tool 50 (e.g., adhesive tape,pliers, tweezers, or other tool allowing multiple carbon nanotubes to begripped and pulled simultaneously);

In block S32, a plurality of carbon nanotube segments joined end to endby van der Waals attractive force is drawn by moving the drawing tool50, thereby forming a continuous carbon nanotube structure 40.

In block S31, the carbon nanotube segment includes a single carbonnanotube or a plurality of carbon nanotubes substantially parallel toeach other. The drawing tool 50 such as adhesive tape can be used forselecting and drawing the carbon nanotube segment. The adhesive tape maycontact with the carbon nanotubes in the carbon nanotube array to selectthe carbon nanotube segment. The drawing tool 50 can select a largewidth of carbon nanotube segments to form the carbon nanotube film, or asmall width of the carbon nanotube segments to form the carbon nanotubewire.

In block S32, an angle between a drawing direction of the carbonnanotube segments and the growing direction of the carbon nanotubes inthe carbon nanotube array 10 can be larger than 0 degrees (e.g., 30° to90°).

Block S22 is different from block S3. The purpose of block S22 is toseparate the carbon nanotube array 10 as a whole from the growingsubstrate 20. The carbon nanotube array 10 separated from the growingsubstrate 20 still in the array shape. The purpose of block S3 is todraw out carbon nanotubes one by one or segment by segment to form acarbon nanotube film or wire from the carbon nanotube array 10 on thesubstitute substrate 30.

In the present method for making the carbon nanotube structure 40, thegrowing of the carbon nanotube array 10 and the drawing of the carbonnanotube structure 40 can be processed on different substrates. Thesubstitute substrate 30 can be made of cheap material, and the expensivegrowing substrate 20 can be recycled quickly and used again for growingnew carbon nanotube arrays 10, thus speeding up the production of thecarbon nanotube arrays.

Depending on the embodiment, certain of the blocks of the methodsdescribed may be removed, others may be added, and the sequence ofblocks may be altered. It is also to be understood that the descriptionand the claims drawn to a method may include some indication inreference to certain blocks. However, the indication used is only to beviewed for identification purposes and not as a suggestion as to anorder for the blocks.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, especially inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including the fullextent established by the broad general meaning of the terms used in theclaims. It will therefore be appreciated that the embodiments describedabove may be modified within the scope of the claims.

What is claimed is:
 1. A method for forming a carbon nanotube structure, the method comprising: providing a substitute substrate, a growing substrate, and a carbon nanotube array comprising a plurality of carbon nanotubes grown on the growing substrate, the carbon nanotube array having a bottom surface adjacent to the growing substrate and a top surface away from the growing substrate, the plurality of carbon nanotubes is substantially perpendicular to the top surface, and the carbon nanotube array being configured for drawing a carbon nanotube structure therefrom; transferring the carbon nanotube array from the growing substrate to the substitute substrate, the plurality of carbon nanotubes is still substantially perpendicular to the top surface after transferring the carbon nanotube array, and the carbon nanotube array still being configured for drawing the carbon nanotube structure therefrom; and drawing the carbon nanotube structure from the carbon nanotube array on the substitute substrate.
 2. The method of claim 1, wherein the carbon nanotube structure is a carbon nanotube film or a carbon nanotube wire.
 3. The method of claim 1, wherein the transferring the carbon nanotube array from the growing substrate to the substitute substrate comprises: contacting a surface of the substitute substrate to the top surface of the carbon nanotube array; and separating the substitute substrate from the growing substrate, thereby separating the bottom surface of the carbon nanotube array from the growing substrate.
 4. The method of claim 3, wherein the surface of the substitute substrate and the top surface of the carbon nanotube array are combined only by van der Waals attractive forces.
 5. The method of claim 3, wherein during the separating the carbon nanotube array from the growing substrate, substantially all carbon nanotubes are simultaneously detached from the growing substrate.
 6. The method of claim 3, wherein the plurality of carbon nanotubes is detached from the growing substrate along a growing direction of the carbon nanotubes.
 7. The method of claim 3, wherein the growing substrate comprises a growing surface for growing the carbon nanotube array, the separating the substitute substrate from the growing substrate comprises moving at least one of the substitute substrate and the growing substrate, a moving direction of at least one of the substitute substrate and the growing substrate is perpendicular to a growing surface of the growing substrate during the moving of the at least one of the substitute substrate and the growing substrate.
 8. The method of claim 3, wherein a bonding force between the substitute substrate and the carbon nanotube array is larger than a bonding force between the growing substrate and the carbon nanotube array, and is smaller than van der Waals attractive force between carbon nanotubes in the carbon nanotube array.
 9. The method of claim 1, wherein a material of the substitute substrate is poly(dimethylsiloxane).
 10. A method for making a carbon nanotube structure, the method comprising: providing a first substrate, a second substrate, and a carbon nanotube array comprising a plurality of carbon nanotubes grown on the first substrate, the carbon nanotube array having a bottom surface adjacent to the growing substrate and a top surface away from the first substrate, the plurality of carbon nanotubes is substantially perpendicular to the top surface, and the carbon nanotube array being configured for drawing a carbon nanotube structure therefrom; transferring the carbon nanotube array from the first substrate to the second substrate, the plurality of carbon nanotubes is still substantially perpendicular to the top surface after transferring the carbon nanotube array, and the carbon nanotube array still being configured for drawing the carbon nanotube structure therefrom; and drawing the carbon nanotube structure from the carbon nanotube array on the second substrate.
 11. The method of claim 1, wherein the transferring the carbon nanotube array from the growing substrate to the substitute substrate comprises applying a pressing force to the carbon nanotube array by the substitute substrate, and a direction of the pressing force is substantially perpendicular to the growing surface.
 12. The method of claim 11, wherein the pressing force is defined as f, and f will satisfy 0<f<2N/cm². 